The present invention relates to alkylated triaryl phosphate ester flame retardants. More specifically, the present invention relates to the use of higher alkylated triaryl phosphate ester flame retardants in polyurethane compositions and to a process for imparting flame retardancy to a polyurethane by incorporating such higher alkylated triaryl phosphate esters therein.
The combination of abundant carbon-hydrogen bonds, large surface area, and open cell structure make flexible polyurethane foams extremely susceptible to combustion. Accordingly, flame retardant additives are often used to reduce the risk and severity of flexible polyurethane foam combustion.
The greatest use of flame retardant additives in flexible polyurethane foams is in automotive applications. In most countries, the interior components of motor vehicles must meet flammability test MVSS-302 or its equivalent.
Known flame retardant additives are volatile or contain volatile components that tend to form an undesirable film on windows as the volatile components are released. This phenomenon is known as fogging.
Automobile and component manufacturers would like to eliminate or at least reduce as much as possible the use of volatile components in motor vehicles and particularly in vehicle interiors.
Notwithstanding the desire of reducing the use of halogens in the automobile industry, flame retardants that are currently used in flexible polyurethane foams typically contain halogens. In fact, tris(dichloropropyl) phosphate is the most commonly used flame retardant for automotive flexible polyurethane foam components. Unfortunately, to date, non-halogen additives are often found to be less efficient than halogenated flame retardants. The use of higher additive use levels of non-halogen additives to compensate for their lower efficiency, contributes to reduced foam physical properties and greater fogging, both of which are undesirable if not unacceptable.
Historically, the first commercially available triaryl phosphates were derived from coal tar and included tricresyl phosphate, trixylyl phosphate, and mixtures of triaryl phosphates. Isopropylated and butylated synthetic triaryl phosphates were later developed as direct substitutes for coal tar derivatives and were mainly used as plasticizers for polyvinylchloride (PVC) compositions. During the development of flame retardant applications, the trend for newer additives was toward higher performance through increased phosphorus content and lower viscosity.
Alkylated triaryl phosphate esters have been used as flame retardants for flexible polyurethane foam for many years. These esters combine good hydrolytic and thermal stability with flame retardant efficiency provided by their phosphorus content. Triaryl phosphate esters are used either by themselves, or more commonly, in conjunction with halogenated additives. U.S. Pat. No. 4,746,682 describes blending alkylated triaryl phosphate ester with brominated diphenyl oxide for use as a flame retardant for polyurethane. The use of isopropylated phosphate esters is referenced in U.S. Pat. No. 4,565,833. These esters contain varying levels of triphenyl phosphate (TPP). The use of triphenyl phosphate has hereto been desirable because it reduced viscosity and contributed higher phosphorus content. Phosphorus is known to contribute to performance as a flame retardant.
Alkylated triphenyl phosphates that have been recommended and used as flame retardants have had phosphorus contents in excess of 7.7 percent. Available butylated phosphates recommended for use as flame retardants have a phosphorus content of at least 8 percent (AKZO-Nobel Functional Chemicals Bulletin 99-94, 1999).
According to the present invention, it has been unexpectedly discovered that higher alkylated triaryl phosphates, having lower phosphorus content, offer superior flame retardant performance in flexible polyurethane foam, combining improved efficiency with a lower propensity to fog.
According to various features, characteristics and embodiments of the present invention which will become apparent as the description thereof proceeds, the present invention provides a method for imparting flame retardant properties to polymer compositions which involves adding to a polymer composition a mixture comprising triaryl phosphate esters represented by the following formula: 
where R1-R15 can independently be located in the ortho, meta or para positions on their respective phenol rings and are, independently, H or branched or linear alkyl groups having 3 to 11 carbon atoms and the mole ratio of the alkylate to phenol in the mixture is at least 0.77, preferably greater than 0.81 and most preferably greater than 0.85
The polymer composition can be any type of polymer composition used to produce synthetic polymers such as thermoplastic polymers including polyurethanes, and can include any other conventional additives and reactants such as catalysts, surfactants, cross linkers, dyes, fillers, etc.
The higher alkylated mixtures of triaryl phosphate ester can be used alone or in combination with other flame retardants including halogenated flame retardants such as brominated and/or chlorinated flame retardants. The higher alkylated mixtures of triaryl phosphate esters can incorporate therein any of the additives and reactants discussed herein, including the other flame retardants.
The present invention further provides a flame retardant polymer composition for producing a foamed article which includes a polyisocyanate, a polyol and the higher alkylated mixtures of triaryl phosphate esters discussed above.
The higher alkylated mixtures of triaryl phosphate esters can be incorporated into the composition alone or added premixed with one of the polyisocyanate or polyol or with one or more of other conventional additives and/or reactants such as catalysts, surfactants, cross linkers, dyes, fillers, additional flame retardants, etc.
The present invention also provides a flame retardant article comprising the reaction product of a polyisocyanate and a polyol with the higher alkylated mixtures of triaryl phosphate esters discussed above incorporated therein.
According to the present invention, flame retardancy is imparted to polyurethane compositions by incorporating therein higher alkylated mixtures of triaryl phosphate esters having higher alkylation levels at 0.5 to 50.0 php (parts per hundred polyol). Higher alkylated mixtures of triaryl phosphate esters according to the present invention are those having triaryl phosphate esters which, on the average, have more alkyl substitution and/or lower triphenyl phosphate content than triaryl phosphates heretofore recommended and used as flame retardants.
The higher alkylated mixtures of triaryl phosphate esters of the present invention are more viscous and lower in phosphorus content than conventional triaryl phosphate flame retardants. Due to their viscosities, the higher alkylated triaryl phosphate esters used according to the present invention have been developed and used as functional fluids such as hydraulic fluids, but have not been used or recognized for use as flame retardants in polyurethane compositions.
Higher alkylated mixtures of triaryl phosphate esters of the present invention are provided as mixtures of triaryl phosphate esters that are represented by the following formula: 
where R1-R15 are, independently, H or branched or linear alkyl groups having 3 to 11 carbon atoms and the mole ratio of the alkylate to phenol in the mixtures is at least 0.77.
During the course of the present invention it was discovered that alkylated triaryl phosphate esters having higher alkylation levels provide better flame retardant efficiency in flexible polyurethane foam compositions than alkylated triaryl phosphate esters heretofore used. This finding is unexpected since the phosphorus levels of esters having higher alkylation levels are lower than those of alkylated phosphate esters that are conventionally used as flame retardant additives.
The higher alkylated mixtures of triaryl phosphate esters of the present invention can be incorporated into polyurethane compositions alone or in combination with conventional halogenated flame retardants. The use of the higher alkylated mixtures of triaryl phosphate esters of the present invention together with halogen containing flame retardants results in unexpected advantages that are analogous to those associated with the use of the higher alkylated mixtures of triaryl phosphate esters alone. Although the higher alkylated mixtures of triaryl phosphate esters of the present invention have a lower phosphorus content than conventional triaryl phosphates, polyurethanes containing blends of the higher alkylated mixtures of triaryl phosphate esters and halogen flame retardants exhibit better flammability test performance than blends of conventional lower alkylated triaryl phosphates and halogenated flame retardants.
The higher alkylated mixtures of triaryl phosphate esters of the present invention may be used alone or in combination with one or more conventional halogenated flame retardant. Preferred halogenated flame retardants for use in conjunction with the higher alkylated mixtures of triaryl phosphate esters according to the present invention include brominated flame retardants such as ring brominated benzoate compounds exemplified in U.S. Pat. No. 5,728,760, ring brominated phthalates, brominated diphenyl oxides, brominated diphenyl alkanes, tribromoneopentyl alcohol, dibromoneopentyl glycol, and hexabromocyclododecane. Chlorinated flame retardants that can be used in combination with the higher alkylated mixtures of triaryl phosphate esters according to the present invention include chlorinated phosphate esters, chlorinated diphosphate esters, PVC powder, and chlorinated paraffins. Examples of chlorinated phosphate esters include tris(monochloropropyl) phosphate and tris(dichloropropyl)phosphate.
The higher alkylated mixtures of triaryl phosphate esters of the present invention can be used in combination with halogenated flame retardants at ratios within a range of from about one part by weight of the higher alkylated mixtures of triaryl phosphate esters to between about 0.2 and about 4 parts by weight of the halogenated flame retardant(s). A more preferred range is about one part by weight of the higher alkylated mixtures of triaryl phosphate esters to between about one and about three parts by weight of the halogenated flame retardant(s).
Polyurethane compositions having improved flame retardancy according to the present invention can be produced by incorporating therein about 0.5 to about 50.0 php of the higher alkylated mixtures of triaryl phosphate esters or about 0.35 to about 35.0 php of a blend of the higher alkylated mixtures of triaryl phosphate esters and halogenated flame retardant(s).
Polyurethanes are prepared by reacting isocyanates with alcohols. Other conventional additives can be included such as other catalysts, surfactants, cross linkers, dyes, fillers, etc. Methods of polyurethane production are well known. The higher alkylated mixtures of triaryl phosphate esters of the present invention can be added to the reaction mixture at the time of reaction or can be pre-blended with one or more of the reactants or additives.
The higher alkylated mixtures of triaryl phosphate esters of the present invention can be used in conjunction with other conventional additives such as catalysts, surfactants, cross linkers, dyes, fillers, etc.
The higher alkylated mixtures of triaryl phosphate esters of the present invention are particularly useful in flexible polyurethane foams.
In the following illustrative examples, tests were conducted to determine the flame retardant characteristics of the higher alkylated mixtures of triaryl phosphate esters and to evaluate their ability to reduce fogging